1. Field of the Invention
The present invention relates to a scroll type compressor. More particularly, the present invention relates to a scroll type compressor which includes a mechanism for transmitting reaction force of a refrigerant gas, applied to an orbiting scroll, to the housing of the compressor and allows the orbiting scroll to make proper orbital movement.
2. Description of the Related Art
Scroll type compressors include a basic structure having a fixed scroll and an orbiting scroll facing each other in its housing. As a rotary shaft rotates, the orbiting scroll makes an orbital movement along a predetermined locus (hereinafter called "revolution"). As the orbiting scroll revolves, the volume of the space defined between the fixed scroll and orbiting scroll decreases to compress a refrigerant gas. In reaction to the rotation of the rotary shaft, the orbiting scroll tends to rotate around its axis (hereinafter called "rotation"). It is however necessary to prevent the orbiting scroll from rotating around its own axis, and to keep it horizontally and vertically aligned in order to optimize the compressor's operation.
Japanese Unexamined Patent Publication No. 59-28082 discloses a compressor which is equipped with an anti-rotation mechanism as mentioned above. In this compressor, as shown in FIG. 9, an orbiting scroll 102, disposed facing a fixed scroll 100 in a housing H, receives the reaction force of a compressed refrigerant gas in compression chambers 106 due to the rotational force of a rotary shaft 104. The rear surface of a base plate 108 of the scroll 102 abuts against a pressure receiving wall 112 of the housing via an anti-rotation mechanism 110.
The mechanism 110 includes a movable ring 118 and a fixed ring 120 which are disposed between the base plate 108 and the wall 112 via races 114 and 116, respectively (see FIG. 10). The movable ring 118 moves integrally with the orbiting scroll 102. The rings 118, 120 have a plurality of pockets 122 and 124, spaced within the circumferences of the rings 118 and 120, at equal intervals, respectively. Rod shaped rollers 126 are supported between the associated pockets 122 and 124 which face each other.
When the scroll 102 and the movable ring 118 rotate in reaction to the rotation of the rotary shaft 104, the rollers 126 roll in the region between the associated pockets 122 and 124. Accordingly, the orbiting scroll 102 performs the orbital movement without rotating itself.
The diameter, d, of the roller 126, which inhibits the rotation of the orbiting scroll 102, the diameter, D, of the pockets 122 and 124, and the orbital radius, r, of the orbiting scroll 102 have the following relation. EQU D=d+r
Therefore, the diameter d of the rollers 126 is defined by the orbit radius r of the orbiting scroll 102 and the diameter D of the pockets 122 and 124.
The end surfaces of each roller 126 slidably contact the races 114 and 116. The compression reaction force applied to the orbiting scroll 102 is transmitted to the wall 112 via the rollers 126. To improve the rigidity of the compressor, either the diameter d or the actual number of the rollers 126 should be increased. Increasing the diameter d of the rollers 126 requires that the diameter D of the pockets 122 and 124 should be increased. The enlarged pockets 122 and 124 require the movable ring 118 and the fixed ring 120 to be wider. However, the wider rings 118 and 120 would enlarge the compressor, and it is not desirable to mount such a large compressor in a vehicle.
To increase the ability for receiving the compression reaction force without enlarging the compressor, it is necessary to increase the number of the rollers 126. However, the increased number of rollers 126 results in an increase in the number of the pockets 122 and 124. The increase in the number of the pockets 122 and 124, which requires a high precision process, leads to longer processing time and higher manufacturing cost.
The end surfaces of the rollers 126 slide along the bottom surfaces of the pockets 122 and 124. With the rollers 126 in close contact with the pockets 122 and 124, inadequate lubrication is likely to occur therebetween which may cause increased friction there.
If any roller tilts in the associated pocket, the peripheral edge of that roller abuts on the bottom surface of the pocket, interfacing with the smooth sliding therebetween. In this case, the peripheral edge of that roller locally wears out, so that the roller would tilt more.
When the inclination of the roller increases, the sliding surface of the roller to the inner wall of the associated pocket becomes an elliptical and the diameter d of the roller changes. This change varies the orbit radius r of the orbiting scroll. This results in inadequate sliding contact between the spiral wall of the fixed scroll and the spiral wall of the orbiting scroll, so that gas may not be adequately compressed.